This invention relates to a method of forming a bonded assembly of ferrous metal members in which aluminum metal is used at the joint between the members to displace nascent zinc from a zinc halide solution at the joint which zinc then unites with the iron of the ferrous members in an alloy to form a secure bond. The invention also relates to an assembly of a plurality of ferrous metal members bonded together in this manner.
The invention also relates to a heat exchanger comprising an assembly of ferrous metal members thusly bonded together.
The most pertinent prior art of which we are aware is U.S. Pat. Nos. 2,179,258; 2,817,895; 3,069,765; 3,287,540 and 3,301,688.
The present invention provides a method of bonding together ferrous metal members by a reaction bonding technique in which aluminum is provided at the joint areas between these metal members and the resulting assembly coated with a liquid bonding composition as disclosed in the above Simpelaar patent comprising a liquid solvent and a zinc halide followed by heating this assembly to a reaction temperature at which the aluminum displaces nascent zinc from the zinc halide to form an iron-zinc alloy at the bond which unites the parts together.
This invention is particularly useful in making heat exchangers of steel and stainless steel because such heat exchangers have been found to be very strong and to have excellent heat transfer characteristics.
Previous methods of bonding ferrous metal elements together included the use of low temperature solders or high temperature brazing. Neither of these is completely satisfactory as the soldered units lack strength and fatigue resistance while brazing processes are expensive, tend to cause distortion in the completed unit and are sometimes difficult to adapt to fast production procedures. The reaction technique of this invention avoids these defects.